The present inventive subject matter relates to lighting apparatus and methods and, more particularly, to solid-state lighting apparatus and methods.
Solid-state lighting arrays are used for a number of lighting applications. A solid-state light-emitting device may include, for example, a packaged light emitting device including one or more light emitting diodes (LEDs). These may include inorganic LEDs, which may include semiconductor layers forming p-n junctions, and/or organic LEDs (OLEDs), which may include organic light emission layers.
Solid-state lighting devices are commonly used in lighting fixtures, including task lighting, recessed light fixtures, ceiling mounted troffers and the like. Solid-state lighting panels are also commonly used as backlights for small liquid crystal display (LCD) screens, such as LCD display screens used in portable electronic devices, and for larger displays, such as LCD television displays.
Solid-state lighting devices may be attractive for retrofit/replacement applications, where devices such as LEDs may offer improved energy efficiency, reduced heat generation, extended life and desired performance characteristics, such as certain color and/or color rendering capabilities. For example, LED bulbs are commonly used to replace incandescent bulbs in down lights and other applications to reduce energy consumption and increase time between replacements. LED-based replacements for fluorescent lamps have also been developed.
FIG. 1 illustrates a typical LED lighting apparatus. The apparatus includes multiple strings of series connected LEDs 10 driven by driver circuits 20. The multiple strings of LEDs 10 may provide different colors, e.g., blue, blue-shifted yellow (BSY), green and/or red. The driver circuits 20 provide current to the LEDs 10 from a current source, such as a power supply 30. The driver circuits 20 may be controlled by, for example, a processor 40 (e.g., a microprocessor or microcontroller). In particular, the driver circuits 20 may be pulse width modulated (PWM) current controllers that are driven by PWM control signals provided by the processor 40. A sensor 50 may detect light produced by the LEDs 10 and provide a measure of the actual color produced by the LEDs 10 to the controlling processor 40. The processor 40 may responsively control the driver circuits 20 to adjust currents passing through the individual strings of LEDs 10 to provide a light output with desired characteristics.